A long-envisioned proposal that would turn a narrow plot of land in southeast Santa Rosa into a public open space with bike paths, walking trails and other recreational amenities is expected to gain additional support Tuesday, when a coalition of community and environmental groups as well as government agencies will for the first time present to the Sonoma County Board of Supervisors a formal proposal to take ownership of the 55 acres.

The city of Santa Rosa has agreed to take primary ownership of the state land, which park supporters hope to transform into a linear open space called the Southeast Greenway. Other partners would manage the land.

The big hurdle remains how the state intends to part with the property, once slated for the Highway 12 extension from Farmers Lane to Melita Road.

The state long ago shelved those plans, and this year it has moved closer to dropping them entirely and declaring the land excess property. Caltrans has yet to say, however, whether it will accede to local requests to donate the land for public open space or sell it on the open market.

“The manner of disposal has not yet been determined,” said Allyn Amsk, a Caltrans spokesman.

The move this week before the Board of Supervisors would establish a formal local interest in the property, lending government support and elevating the grassroots lobbying campaign for the greenway.

“The letter of intent is designed to get formal approval and buy-in from our governing bodies,” said James Nantell, the county’s Regional Parks deputy director. The agency has been involved in conversations about the parcel since January. “It’s not a binding agreement yet, but we want to formalize what we’re trying to accomplish with the various agencies, so we’re closer to spelling out in a contract what everybody will be doing.”

In addition to Santa Rosa, the proposal before the Board of Supervisors includes preliminary agreements with the Sonoma County Water Agency, the county Regional Parks department, and LandPaths, the Santa Rosa nonprofit agency that helps acquire and manage open space.

Organizers with the Southeast Greenway Campaign, the primary group leading efforts to take ownership, said Tuesday’s presentation represents progress.

“We don’t have anything worked out with Caltrans yet regarding the process for transferring the property,” said Bob Gaiser, an organizer with the community group. “But we’re putting out this preliminary statement. There will be lots of details to work out when things get moving.”

Following Tuesday’s action at the Board of Supervisors meeting, greenway organizers plan to begin fundraising to purchase the land. The city of Santa Rosa does not intend to put up any money toward the acquisition.

“We actually took City Council action during our budget process to set aside $100,000 to help with various kinds of planning and regulatory things,” Santa Rosa City Manager Kathy Millison said. “But not for the land.”

Millison said a combined countywide effort will help in drawing Caltrans to the table. “When dealing with a state agency like Caltrans, they really want to see local agencies and community groups work together so they only have to deal with one voice,” she said. “Since most of the property is in the city of Santa Rosa, we will take that lead as facilitator of that conversation.”

State transportation planners bought the southeast Santa Rosa land in the 1950s and ’60s when the area of the city was sparsely developed. The intent was to build a 2-mile freeway bypass from Farmers Lane over Spring Lake, rejoining Highway 12 near Oakmont.

Spring Lake since has become a county park and popular recreation area and Bennett Valley neighborhoods filled in around the land planned for the freeway. Santa Rosa residents resoundingly rejected the bypass, including a bridge over Spring Lake, saying it would be environmentally damaging and unnecessary.

Park advocates have since touted the idea of a greenway leading east from Farmers Lane. The corridor could serve as a link between the city and the park complex on its eastern edge, including Spring Lake, Annadel State Park and Howarth Park.

“Recreation and ecotourism are increasingly becoming important sectors of our economy, and this will add even more amenities,” said Linda Proulx, co-chair for the greenway campaign.

You can reach Staff Writer Angela Hart at 526-8503 or angela.hart@pressdemocrat.com. On Twitter @ahartreports.